Quillworts

Sporophyte (=spore-producing phase)

Vegetative features

Stem

• Brown, lobed, corm-like stem called a rhizomorph

• Tiny amounts of wood (secondary xylem) and bark (phellem) are produced inside rhizomorph

  • **Quillworts are the only living spore-bearing plants with secondary growth** 

•  Bipolar growth: stems act as roots and shoots

Leaves

• Tufted, grass-like microphylls / lycophylls 

• Each leaf is also a sporangium-bearing leaf (sporophyll)

• Sporangium with a ligule

• Isoëtes is capable of C3 photosynthesis and CAM photosynthesis (Wickell, 2021).

  • When terrestrial, these plants absorb and fix carbon dioxide as C3 plants

  • When aquatic, these plants use CAM photosynthesis to concentrate CO2, since they are living in water with low amounts of carbon dioxide or bicarbonate

Roots

• Roots branch dichotomously after they emerge from the rhizomorph

• Roots have an air canal running through the root, similar to other wetland plants

• Isoëtes can absorb carbon through roots (**unique among plants**)

Geologic range

• Rhizomorphic lycophytes, which include quillworts and lepidodendrid scale trees date back to the Late Devonian

• Plants resembling the quillworts, Pleuromeiales, date back to the Triassic Period

Chaloneria cormosa †

• Pigg & Rothwell 1983

• Late Pennsylvanian of Appalachian Basin

• Unbranched, upright plants (~2m tall) with  rounded base, bisporangiate fertile regions, and  secondary growth

• Leaf bases robust, parichnos  present, leaf cushions absent

• Exarch protostele,  medullated above basal region, with radial plates  of xylem parenchyma separating groups of tracheids

• Leaves with blunt keel and two bands of sunken stomata on abaxial surface of lateral laminae

• Thick-walled, trilete megaspores with auriculae, conforming to sporae dispersae genus Valvisisporites

• Microspores trilete and bladdered  often preserved in tetrads; conforming to sporae dispersae genus Endosporites

Clevelandodendron ohioensis †

• Chitaley & Pigg 1996

• Late Devonian (Famennian) of Ohio, USA

• An unbranched, slender (2 cm wide) plant with a partially preserved plant base bearing thick appendages at the base; apically the plant bears a compact, terminal ovoid bisporangiate strobilus

• Sporophyll/sporangium complexes attached to axis at 90 angle and extending downward at 60 angle to axis, with prominent distal laminae;

• Clevelandodendron demonstrates that slender unbranched lycopsids with an isoetalean  plant habit similar to the Carboniferous genus Chaloneria and the Triassic genus Pleuromeia were present as early as the Late Devonian. 

• The early occurrence of this unique habit suggests that diversification within the  isoetalean clade sensu Rothwell and Erwin (including both Isoetales and Lepidodendrales) was well established prior to the  Carboniferous

Cyclomeia †

• White, 1981

• Early Triassic of Australia and Tasmania

• Produced terminal bisporangiate, penduculate cones of the Skilliostrobus-type

• It possessed helically-arranged, wedge-shaped sporophylls with an adaxial groove containing obovate sporangia (Taylor & Taylor 1997)

• The cones was 8 cm wide, and about 4 cm long

C. longicaulis †

• White, 1981

• Originally named Pleuromeia longicaulis 

C. undulata (White, 1981) †

Cylostrobus †

• Retallack, 1995

• Early Triassic of Australia

• Similar to Pleuromeia, but with very compact and round cones

• The genus Cylostrobus was erected for the compact cone only, in the paleobotanical system of form genera, but these small plants are well enough understood that the name Cylostrobus is used for the whole plant

C. indicus †

• Middle Triassic 

C. ornatus †

• Late Triassic of Argentina

• Petrified cone specimens originally named Austrostrobus ornatum (Morbelli & Petriella 1973)

C. sydneyensis †

• Middle Triassic 

Ferganodendron †

• Dobruskina, 1974

• Triassic

• Resembles Pleuromeisa and Sigillaria

• 20-30 cm in diameter and covered with numerous, elliptical-rhomdohedral leaf bases that are helically-arranged

• Leaves are small and only found don distal portions

Lepacyclotes †

L. cicrcularis †

L. convexus †

L. ermayinensis †

L. zeilleri †

Leptophloeum rhombicum †

• Li et al. 1986; Wang et al. 2015

• Late Devonian (Frasnian) Huangchiateng Formation of Hubei, China

• 300–400 mm in width; 10–25 m in length

• This plant shows the lepidodendroid phyllotaxy 

• The leaf cushion inter-areas are absent.

• Leaf cushions are rhombic, about 8–10 mm high and 10–12 mm wide, and the height-to-width ratios appear to be higher in the lower part of the trunk.

• In a few instances, a tiny dent can be observed in the upper corner of leaf cushions, possibly representing a ligule pit. 

• There is an oval leaf scar about 3.0–3.5 mm long and 1.5–2.0 mm wide, approximately in the center of the leaf cushion.

• Sporophylls are peltate in outline aggregated into a strobilus

• Sporangia are elongate to ellipsoidal

Lycaugea edieae †

• Meyer-Berthaud et al. 2021

• Late Devonian (Famennian) of Australia

• Axis with helically arranged deciduous leaves

• Leaf bases showing a parichnos below a small leaf vascular trace. 

• Leaf trace and parichnos located in the upper part of the leaf base.

• Parichnos in leaf bases large, filled with contiguous parenchyma cells showing thicker walls towards the outer region of the leaf bases. Primary vascular tissues consisting of a medullated stele.

• Protoxylem continuous, forming a thin ring with a smooth outer border around the metaxylem.

• Primary cortex three-zoned, with a wide middle cortex and a homogeneous outer cortex bounded externally by a hypodermis consisting of narrow cells with heavily thickened walls

• Leaf traces in the outer cortex associated with the radially elongated abaxial cavity of the parichnos.

Pleuromeria †

• Triassic of Germany, France, Spain, Russia, China, and Australia

• It was an opportunistic pioneer plant that grew on coastal mineral soils (halophytic) with little competition as monotypic stands (Retallack 1997)

• Some specimens from China indicate that those species lived in more xeric, inland sites, near desert oases (Wang & Wang 1982)

• Pleuromeia was a herbaceous plant that probably lacks secondary tissues, although there may be some evidence for secondary cortical tissues

• and has an unbranched stem of 30 cm long and 2–3 cm wide in the earliest species, to around 2 meters long in later species

• The stem supported microphylls that are discarded in the lower part of the stem

• It had a 2-4 lobed bulbous base to which numerous adventive roots are attached

• Pleuromeia produced a single large cone at the tip of the stem or in some species many smaller cones

• The top of the cone carries microsporophylls, the lower part megasporophylls, and both types may be interspersed in the middle.

• Sporophylls are shed from the bottom up

• Both types are obovate, with a round to ovoid sporangium and a ligule nearer to the tip on the upper/inner side

• The trilete microspores are hollow, round and 30–40 μm in diameter

• Megaspores have a layered outer skin with a small trilete mark, are also hollow, round to ovoid and up to 300–400 μm in diameter

• The anatomy of the spores in Pleuromeia is comparable to that of Isoëtes and substantiates the assumed close relationship between the Pleuromeiaceae and the Isoëtaceae.

P. dubia † 

• Seward; Retallack, 1995

• Late Early Triassic

P. epicharis  † 

• Wang & Wang, 1990

• Triassic of Shiqianfeng Group of north China

P. hataii †

• Kon'no, 1973

• Late Early Triassic

P. jiaochengensis †

• Wang & Wang, 1982

• Early Triassic of Shanxi Province, China

• Smallest species known, at only 50cm tall with 3mm long microphylls

P. rossica †

• Neuburg, 1960

• Transferred to the genus Lycomeia (Dobruskina 1985)

P. sternbergii †

• Corda, 1839; Grauvogel-Stamm, 1990

• Early Triassic of Germany

• Covered in leaf bases to near the base of the plant

• Exhibited 2 types of leaves in a lax position (subhorizontal)

Sublepidodendron †

• Nathorst, 1920; Hirmer, 1927

• Early Carboniferous of Norway, China

•  impressions of very thin bark layers or entire tubes of bark that remained when the plant organs were macerated prior to fossilization

• Arborescent,heterosporous lycopsid known from trunk, branches, and cones

• Leaf bases are spirally arranged, fusiform in outline, with a vascular bundle scar and keel

• The trunk has an intrastelar parenchyma concentration (pith), exarch primary xylem, and secondary xylem

• The branch anatomy varies from exarch primary xylem with a small, centrally located pith, to a solid exarch primary xylem strand

S. grabaui 

• Wang and Xu, 2005

• Famennian of Jiangsu, South China

S. mirabile  †

• Nathorst; Hirmer, 1927

S. songziense †

• Chen 1977; Wang et al., 2003

• Late Devonian of China

• Monocaulous trunk growing from a stigmarian rhizomorph, the trunk bearing biseriate, sub-opposite to possibly alternate lateral branches that expand by means of isotomous to slightly anisotomous dichotomies, forming an excurrent canopy

Tomiostrobus †

• Retallack, 1997

• Early Triassic of Australia and Russia

• This plant was especially widespread in the aftermath of Permian Triassic mass extinctions

• Tomiostrobus is preserved as whole plants closely spaced within bedding planes, and lived as an early successional weed in lake and pond sedimentary environments, like living Isoëtes

• Unlike living Isoëtes, Tomiostrobus formed closed cones with sporophylls that were distinctly shouldered and woody

• This may have been an adaptation to heavy grazing by herbivorous therapsids (Retallack 1997)

T. australis †

T. gorskyi †

T. migayi †

T. mirabilis †

T. polaris †

T. radiatus †

T. taimyrica †